Grinding and lapping machine



F. C. WEAVER.

GRINDING AND LAPPING MACHINE. APPLlCATlON FILED NOV. 11, I920.

. 1,422,5U5. Patented July 111, 1922.

3 SHEETS-SHEET I.

; un mmE 24 l F. c. WEAVER. GRINDING AND LAPPING MACHINE.

APPLICATION FILED NOV\ II, I920.

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F. C. WEAVER.

GRINDING AND LAPPING MACHINE. APPLICAHON FILED NOV. 11 1920.

1,422,505. atented uly 11, 1922.

3 SHEETS-SHEET 3.

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\ V 4 FLOYD CALVIN WEAVER, OF WASHINGTON, DISTRICT OF COLUMBIA.

To all whom it may concern:

Be it known that I, FLoYD C. WEAVER,

a citizen of the United States, residing at- .Washington, in the District of Columbia,

have invented certain new and useful Improvements in a Grinding and Lapping Machine, of which the followingis a specification, reference being had therein to the accompanying drawings.

This invention relates to a grinding and lapping machine and the object is the production of a machine for the making of precision true plane surfaces ofglass or other crystalline materials.

Another object of the invention is the production of a ,machine for producing and finishing the precision true plane surfaces necessary for test of gage blocks, both in the process of making and when they are removed from the machine for use. 4

A still further object of the invention is the construction of a machine which is I production of a machine whereby optical,

true, plane surfaces are produced, necessary for-the most highly precise method of length comparison by light interference methods which are now universally established. In conjunction with the aforestated means of precise measuring, is the production of permanent standards of length in duplicate,

adapted to the above method of test and also equally suitable for industrial snap gage checking, etc., as is required in recision tool and machine work, roller and ball bearings, watch making, etc.

With these and other objects in view. my

invention comprises certain novel combinations, constructions and arrangements of parts as will be hereinafter described, illus trated in the accompanying drawings, and more particularly pointed out in the appended claims.

In the drawings: 0 Figure l is a top plan view of the polish mg or lapping or grinding machine.

Specification of Letters Patent.

not less thanthat of the recessed disc.

Patented July llll, 922..

Application filed November 11, 1920. Serial No. 423,371;

.4-4, Fig. 1, and looking in the direction of the arrows.

Figure 5 is a transverse, sectional view showing the method of mounting the gage blocks in a circular disc form upon an optically flat surface, thegage blocks being separated by a hard wax or. resin, or a perforated metal plate 63 bedded in the hard wax for holding blocks in addition to the resin, and the outside supported. by a brass or metallic retaining band fitting tightly to the flat supporting surface and being of a height slightly less than the gage-block.

This-mounting of the gage blocks,. with resin in the retaining ring, or also a metal perforated spacing plate added, all fitting tightly upon the optical flat surface, are shown held rigidly in position by wedges between the outer ring fastened securely to the plate mounted on the driving spindle. Also this outer ring secures the position of the optical fiat surface by wedges, as shown.

Figure 6 is a vertical section of the circular blocking arrangement for glass and crystalline materials. The faces of discs to be worked are turned downward upon a master fiat surface, the discs being set into recesses out in a disc of similar glass of the same thickness and the tops of the intervening spaces closed by paraffin to be water t ght. An outer stiff retaining metal band is set upon a ring, forming an open topped" vessel on the master flat surface into which plaster Paris is poured over top of discs. Over the discs set into the recessed plate is set a second plateof glass of same thickness as the discs and at a distance above them equal to at least one quarter their thickness and parallel to the same, and of a diametigr stiff, webbed, thin metal plate with recess for driv ng pin is set into top of block before the plaster of Paris set hard forming a rigid block. When plas er has hardened the flat ring is removed and plaster trimmed away in relief from recessed plate, I

gage block 'a top transparent flat and a projecting portion of the master flat surface upon which the gages are mounted, second the parallel fringe method using a top transparent flat for testing flatness of individual blocks or glass discsand also the agreement of gage blocks with. a standard block which-is set upon projecting edge of the master fiat surface. This latter method is for duplication of standard the parallel fringe method is used when gage blocks are still much too long i. e; 0.002 millimeter or .0001 inch and less, and the circular fringe or optical plane parallel test when the differences between gage block and the standard block are in the orderof .0005 millimeter or .00002 inch down to .000001 inch. It is pointed out that when convenient the wedges are removed fI'OIIlLthG outer ring to give a clear space for the optical testing against the projecting edge of the master flat surface.

Referring to the drawings by numerals, 5 in Fig. 1 is the sole power drive to the lapping machine, belt or direct connected motor, etc. In Figs. 1, 2, 3 and 4, power drive 5 is positively connected by gearing or chain belt to both vertical spindles carrying plates 6 and 9. Plates 6 and 9 are thereby driven in a fixed relation to each other and are so constantly maintained in that relative rotation. Plate 6 and plate 9 each carry vertical bearing posts 7 and 10, respectively, which are capable of adjustment in such manner as shown by T slot 11 of plate 9, so as to have adjustment of stroke or throw when plates 6 and 9 revolve about their fixed vertical axes, which bearings are made rigid with machine? body. Plate 9 is shown in sections 22 Fig.2 and 4-4 Fig. 4 to be capable of adjustment position of throw of post 10 relative to that of post 7. Plate 9 is shown in section 2-2 Fig. 2 to rest upon machined plate 35 which is rigidly fastened to the vertical spindle 38. Thus plate 9 can be set by index marks at section 44 and when desired setting is made, plate 9 is firmly clamped in fixed relation by screws 58 to plate 35.

The lapping plate 27 is thus driven by the tool in '26 actuated by posts 7 and 10 connecte to 26 by thrust bars 14 and 18,

' respectively, with a flexible joint 16. Thrust bars 14 and 18 join posts 7 and 10, respectively, with hinge joints as shown at post 10, also length of .both bars 14 and 18 are mediate elliptical strokes of the gages, in process of working;

adjustable by locking double screw turnbuckles or telescoping slides with clamping screws 15 and 17, respectively. The tool pin 26 is thereby adjustable in stroke from practically a straight line to a circle, with interentire range of eccentriclties. Thus the strokesxof tool pin 26 actuate the lapping plate 27 over the work (as blocks 28) mounted on plate 30. The amount of lapping of lapping plate 27 can be distributed in any manner desired over work mounted on late 30 by both adjusting strokes of tool pin 26 and by rotating plate 30 about its mounted in rigid bearings of the machine frame. Pressure on lap 27 is obtained by adding cylindrical weights 59 on tool pin 26.

Plate 30 is driven positively by gearing, or chain belt, through a friction clutch 20 from shaft 12 by bevel ears 13 on shaft 12 and 33 on shaft 19. I haft 19 is thereby capable of driving plate 30 through bevel gears 22 and-41 Or to be independent and locked in position by friction clutch 20.

-Also plate 30 can be actuated by hand vertical axis 42 v gear'21 is then engaged to drive bevel gear 22 and 41 and plate 30. Thus it is shown how plate 30 may be driven automatically through clutch 20, and also. by disengaging 20 and engaging clutch on bevel gear 21, plate 30 is then driven by hand wheel 24.'

The following adjustments are special to this machine, first, adjustment of length of strokes or throw of posts 7 and 10 of driving plates 6 and 9, respectively by T slot 11; second, adjustment of relative position of post 10 on plate 9 with respect to position of post -7 on plate 6 by means of a plate 35 and clamping screws 58, shown in Fig. 2; third, adjustment of the length of bars 14 and 18 by turn-buckles or sleeves 15 and 17, respectively, so provided with locking nuts that position of strokes of tool pin 26 may be altered or changed at will of operator, 7

Certain features of this machine of importance are; plane disc laps or grinding tool 27 and master flat plates 43 as can be readily turned and surface ground; the machine laps and finishes its own plates, as

well as using these same laps, in producing optical flats, etc., and gage blocks, and the machine gives an optical polish to both metal and glass surfaces which gives full use of the optical tests; the most precise optical tests are applied to work on the machine cally holding the gage blocks 28, is shown in Fig. 5. These blocks 28 are set firmlyupon the top surface of master flat surface 43 and in intimate contact. This process of setting (sometimes called ringing) is facilitated in case of transparent blocks where setting by; black fringe indicates the closest contact to master surface. Blocks 28 are first prepared by preliminary (grinding and machining to have general 1mensions of final block, with small excess stock to facilitate the final precision lapping.

- This also applies to metallic and glass or crystalline blocks as well. Blocks 28 are placed in contact with master flat surface 43 in uniform or symmetrical arrangement inside the brass ring 29, and with a small space between each block28. Ring 29 fits accurately upon top surface of 43 and is slightlyless in height than finished length of blocks 28. Blocks 28 whenarranged on v43 are held firmly in position by the heavy lapping tool 26 placed upon them. Ring 29 is held concentric with 43 by means. of wedges 45 bearing against the plate ring 44. This plate ring 44 is in,turnwedged concentric and firmly to the main spindle plate 30. Plate 30, Fig. 5, is a lane lapped plate and turned and finished cy indrical edge and is rigidly fastened tothe vertical spindle 42 of Fig. 3. Ring 44 has a shoulder bearing on top drical edge of 30 and with a small amount of clearance. Thus it is seen that 44 is then held firmly and rigidly on 30 .by wedges 59. The master flat surface 43 with one flat lapped surface in contact with the top lapped surface of 30 is held rigidly by wedges 46 concentric with 44, and also with 30. Thus the entire mount is held rigidly in concentric position ready for lapping,

. etc., and also capable of being entirely dismantled, cleaned, etc.,' and returned pre-fcisely to its original condition and adjustment. With blocks 28 so mounted upon master surface '43 as above described, the

intervening space between blocks is poured full of melted hard wax, resin or compounds of resin and shellac, etc., as indicated by a spout 47 at points around the space between ring 29 and the lap 27 which prevents blocks 28 from lifting away from master surface 43 or changing from placed positions. Wax is not filled into spaces between blocks and ring higher 'thanbrass ring 29. When wax .60 hardens, lap 27 is removed until lapping operation is started when the lap 27 is returned to position'as shown in Fig.

of 30 as well as on the outer cylin- .clampingl by wedges 46 produces no deflection wit in absolute methods of testing of top surface. Also, when master surface '43 is made of glass, etc., a thin non-heat-conducting layer is placed between it and plate I 30, and plaster Paris cast into groove otherwise occupied by wedges 46 and substituted for them.

Optical interference tests with masterplate s readily determine the flatness of 43 and also tops of blocks 28. During progress of lapping, as will be hereinafter fully described, blocks 28 can be compared by optical interference test against outer projection surface of 43 beyond ring 29 for uniformity of height or agreement with a given standard block, or for flatness of top surface, and also lapping plate 27 can be frequently tested in like manner for flatness of surface. "Wedges 45 are removed when making optical interference tests to master surface 43; however, it is found inpractice-that necessary wedges 45 occupy a very small part of the circular zone of 43 and it is seldom necessary toremove them at all. Ring 44'has the two inner surfaces bearing against wedges slightly conical to facilitate the wedging action of 45 and 46. Outside of 44 is made smooth and free of burrs and projection portions to facilitate cleaning; also, to enable operator in last stages to give smoothness to hand operation of plate 30 by using hand in addition as a delicate brake on mm 44.

One endlof gage blocks 28 is first lapped as above described for a flat surface and polished; second, the first finished surface of 28 is set on 43 similarly to operation for first surface and the second surface is then lapped for flatness and for parallelism; The check 'for parallelism and for given thickness or separation of two parallel surfaces of 28 will bedescribed in treatin 'of Fig. 7. The lapping plate 27 for metal ic bodies 28 has thick metal discs reinforced by webs and a rim at. back and ahub with recess for ball .to under lap-ping surface from the recess onback of 27 formed by the hub, webs and rim. Lap 27 is also used in lapping master surface 43 as well as plate30 when setting up the machine. The lapping plate 27 for glass, etc, is changed to a form described by. Fig.

'6, where the physical characteristics of glass,

etc., require fundamentally different consideration and treatment, however the same and processes of working and lapping apply throughout after the blocking is accomplished.

It is to be noted that ring 29 and ring 44 are provided with divisions and designating marks on outside rim every ninety degrees, also on outer cylindrical edge of master surface 43. This enables and facilitates repeating relative settings and particularly in recording and operating on particular zones and sectors of blocked work on surface 43, as is necessary in lapping parallel surfaces in removing geometrical errors from flat surfaces.

In the final lapping or finishing, an optical polish is given blocks 28 by coating the surface of lap 27 with a compound of pitch, resin, beeswax and rouge in a layer about one quarter of an inch in thickness; and the polishing operation is then carried out precisely as the previous lapping operations. The lap is fed with more rouge mixed in lime water and soda through the small holes 61 in the lap 27. v

Fig. '6 shows the method and process of blocking glass and crystalline materials for precision flat surfacing. Also, the fundamental starting point. as for metallic lapping is the master fiat surface 43. In most refined working of glass, the master surface 43 is made of annealed glass, while for working metallic bodies master surface 43 is made of metal and optically polished. In blocking discs of glass 55 for making glass master surfaces, they are set with the face to be worked against master surface 43 with a very small amount of volatile oil, naphthalene, benzine, etc., and set in recesses cut in a larger disc 54 of similar glass of the same or greater thickness, preferably the same thickness, also set against surface 43 in a similar manner to 55. Discs 55 are set concentric with the slightly larger recesses cut in 54. Concentricwith 54 is set the auxiliary blocking--ring 48 against surface 43. Upon this ring 48, which is carefully machined, is set the metal binding ring band 49 fitting tightly to top of ring 48 so as to hold the liquid pla ing. With blocks or discs 55 placed with 54 on surface 43 and with band 49,0n ring 48 the top edges of' space between discs 55 and recess in 54 are painted with a brush and melted parafiin or beeswax as 62 so as to prevent plaster Paris mix from flowing down into recess. Also great care is to be exercised in keeping the paraffin or beeswax from entering down appreciably into" this space. The outside edge of disc 54 is also lightly painted with parafiin or beeswax to revent plaster Paris mix from entering etween surfaces of 54 and 43. The plaster Paris is then poured into the block until it covers top of 54 and 55 by approximately one half their thickness. The plate 50 of with paraffin.

ster Paris when castfined glass fiat and similar glass of at least the same thickness of 54 and 55 and of a diameter slightly larger than 54, is set above the plates 54 and 55 parallel to them and at a separation of not over one half their thickness before the plaster Paris begins to set. Disc 50 is painted with a thick paraffin coat about one sixteenth of an inch ,on only the outer cylindrical portion of the disc before setting into the plaster. Also disc 54 is previously treated likewise on outer cylindrical surface and then set on master surface 43. The plaster Paris is allowed to harden and dry just coming to the top edge of disc 50' but not on top face of disc. The edge of plaster Paris between disc 50 and band 49 is then painted with paraflin to be water tight and sealed. The secondpouring of plaster-Paris is now made being just enough to completely fill remaining space when top blocking plate 51 is pressed down flush with the top edge of band 49.- Plate 51 is a thin metal, preferably, aluminum, plate stifiiy ribbed at back cess for the hard wooden block 52, which carries tool point. The bottom face 51, as well as the outer cylindrical edge, "is ac curately turned, also, top edge of rim to be parallel to bottom face and the edges of center recess to be in same plane as rim edge. This enables the plate 51 being set in plaster accurately and concentrically by wedges and by placing a heavy lapping tool with fiat face bearing down on top rim edge of 51 causing the plate to sink in plaster until of band 49. In this position, the plaster is allowed to harden and dry,'when plaster is hardened and dry lapping tool is removed and exposed ring of plaster sealed water tight The entire block is, now removed from master surface 43 and ring 48 is also removed by light tapping downward away from hand 49. The plaster ring between 54 and 49 is trimmed to relieve away from 54, i. e., as relieving type, about one sixteenth inch below the edge of 54 formerly in contact with 43. This ring of plaster, when so relieved, is impregnated with melted paraflin to be water tight. The remaining spaces between discs 55 and walls and edge with a circular reof the recesses in 54 are filled with melted beeswax or res1n. This gives the edge support to discs 55. When disc 54 is left one solid glass-disc, itis made up and used as a master surface in place of 43 and set up in an identical manner for the most'replane parallel working as hereinbefore described metallic gage blocks 28. Glass plane parallels similar to blocks 28 are worked in precisely the same manner, the lap 27 becomes the solid disc of glass blocked as described, Fig. 6, and the I mastersurfaoe 43 is replaced by a second solid disc of glass blocked as in Fig. 6, and

100 face of lapping tool rests upon the top edge 1 upon which the glass bodies are treated as described for metallic bodies 28. Incase of plane surface bodies as 55 above described method of blocking Fig. 6, the finished block in band 49 is turned glass side up on plate 30 and treated as master plate 43 when being lapped by a tool 27, only in last stages a glass lap is used in place of metal one.

allels as will be described for Fig. 7, alsofor the auxiliary tests of blocks 28 removed from machine. It is also pointed out that' these glass flat surfaces are fundamental in all precision optical equipment testing, etc.,

hence a field of application quite as wide as ing its applications to metallic gages, etc., and quite removed including practically every scientific field of endeavor as well.

The specific points of claim for the process of blocking Fig. 6 is; first, a method of casting or setting a disc of lass, etc., in plaster block without mechanlcal compression and deflection stresses; second, a method of setting the discs 55 and54 to' have a flow of heat upon temperature change in a direction normal to precision flat surface by employment of a buffer and insulator barrier disc 50 in Fig. 6 for heat coming to or away from 54 and 55, the action being in a sense that of insulation and also that of an equalizer, the paraflin at edges. of discs 50, 54 and 55, acting as heat insulator with the ring of dry plaster Paris and also relieving the compression of the plaster Paris on ed e of discs; third, that by the method of bloc ing, Fig. 6, using a lapping disc so blocked in place of27 and the discs 54 and 55 or one solid disc as-54 and for plane surface workas 43 or for plane parallels of glass, etc., the effect of the heat produced in the lapping and polishing process and that which may come from external room sources will be to cause only geometric errors due to heat expansion. These errors are chiefly the surfaces changing from one very long radius of curvature to a longer or shorter radius, and these errors are dlrectly measured and interpreted by interference testin with a master optical flat surface, enabling a direct adjustment of lappingeffort on the machine i. e., stroke of tool pm 26 and rotation of plate 30 to reduce the errors of the surface within the range of the oscillating heat and expansion changes found for a given disc form for agiven temperature. It is also stated that different disc forms, i. e., discs of the same diameter but of different thickness behave far out from any ratio of their dimensions when the flatness of surfaces or the flatness and the parallelism of its two surfaces are considered under the effect of temperature changes and with the methods of a' plying heat or drawing heat ayvay to anoter mass or body.

In Fig. 7 is shown the method of optical interference testing upon the gage blocks 28 in process of working. It is to be noted that the application of test by optical flat discs 56 is very readily and quickl applied. The lap 27 being removed and t e top surface of blocks 28 cleaned, also the edge of 43 projecting beyond the band 29 is thoroughly cleaned. The complete test" of work in progress is then as follows. First, a test of flatness of blocks 28 by placing optical flat 56 upon 28 and gently pressing downward until intimate contact is obtained showin for flat surfaces of 28, alternate straight bright and dark lines parallel to each other and equally spaced. Second, the test for parallelism of top and bottom surfaces of blocks 28, by placing 56 upon top of 28 and letting one edge project over such that outer part ofsurface of 43 can be seen along AA through projecting portion of 56, so that if 56 is pressed firmly on 28 until contact is 'so intimate that no interference bands are seen then upon sending monochro matic light in the direction of AA toward surface of 43, a transparent glass at M will transmit light along A-A also reflect the circular fringe system shown above of alternate light and dark rings produced between surface of 56 and 43 and seen at E or with light source at E system is viewed along AA, so upon moving position atE keeping M fixedin adjustment parallel surfaces upon 28 'will be indicated by this system of rings remaining unchanged, if blocks 28 are not parallel surfaced the ring system will change hence, if m is known the an 1e of wedge of" surfaces is at once known. r1ed around the entire surface of 43. and band 29 and the position of highest and his test-is carlowest blocks noted for further lapping.

Third, the test for agreement to a g ven standard block, 57 is made with anoptical flat 56 placed carefully in as intimate contact as possible with at least two blocks 28 and the standard block, 57 in such a manner that a. portion of outer-free surfaceis included between, the blocks and. then the plane paralleltest is applied as above descrlbed using the circular fringe system, the-interference. occurring between 43 and lower surface of optical fiat 56, i. e., -along line B-'.B. The angle of wedge, above described always in-. di'cates the higher or longer block, i. e., 28

ice

or 57, and how much the'length must be reduced. This method of working, above described, gives a direct measure of the errors numerically and by timing the rate of lapping for the condition of working maintained constant, the error is readily reduced to the limits of measurement-and the intrinsic physical characteristics of the blocks 28 and 57 and the optical fiat 56.

Practice shows that the optical flats 56 neednot be larger than one half the diameter of band 29, as the larger flats have temperature characteristics that outbalance unfavorably 'the convenience of covering a large area possesses for the general routine of the process. Also it is well to have band 29 not over three fourths the diameter of 43, and it is more advantageous to have 29 two thirds the diameter of 43.

It is pointed out that for gage blocks 28 1 made of glass, i. e., plane parallels, the tests are more direct and simple since the media of block is transparent and the plane parallel test is directly applied. The agreement test to a standard block 57 however is carried out in precisely the same manner'as above described for metallic blocks 28.

While I have described the preferred embodiments-of my invention, and have illustra-t'ed the same in the accompanying drawings, certain minor changes or alterations may appear to one skilled in the art to which 'this invention relates, during the extensive manufacture of the same and I, therefore, reserve the right to make such alterations or changes as shall fairly of the appended claims.

What I claim is: i

1. In a machine of the class described, the combination of a pair of plates, means for rotating .said plates at the same rate of speed, a work-supporting plate contiguous tosaid pair of plates, means for driving said work-supporting plate at the same speed the first-mentioned plates are driven, a lapping plate contiguous to said work-supporting plate,

means connecting one of the first-mentioned plates to said lapping plate for mov through the 'me ing the lapping plate over the work-supporting plate, and means adjustably connecting said just-mentioned connecting means to the other plate of the pair, whereby movement of the lapping plate with reference to the work-supportin plate will be controlled plate. 7

2. In amachine of the class described, the

' combination'of a pair of plates, means rotatling said platesat the same speed, a worksupportmg plate, meansrotating said work supporting plate at the same "speed as the first-mentloned plates, a lappin plate over said work-supporting plate, an means con n'ecting said lapping'plate 'to :both of said .5 ttfirst mentioned plates for moving the lapfall within the scope ium of said first mentioned porting plate is controlled at two points of I the machine.

4. In a machine of the class described, the combination of a plurality of plates including a work-supporting plate all rotatin at a fixed speed, a lapping plate-adapter? to move with respect to one face of the worksupporting plate, means for stopping the movement of the work-supporting plate while the other plates are moving in time relation, and manually-operated'means for moving the work-supporting plate while the other plates are in continuous movement independent of said manually-operated means.

5. In a machine of the class-described, the combination of a plurality of plates includin a work-supporting plate, means for drlving all of said plates at the same speed, a lapping plate over said work-supporting plate, means connecting the lapping plate with one of the first-mentioned plates for causing the lapping plate to move when movement is imparted to the connected plate, and means adjustably connecting the lapping plate to another of the plates for controlling the movement of the lapplng plate with respect to the work-supporting plate. N

6. In a machine of the class described,

the combination of. a series of plates includinga work-supporting plate rotated at the same speed, a lapping plate over said worksupporting plate and moved or driven with respect to the work-supporting plate by two of the first-mentioned plates, means for causing the work-supporting plate to remain idle independent of the movement of the other plates, and means for manually moving or drivin the work-supporting plate at a speed di erent from the speed of movement of. the other plates.

7. In a machine of the class described, the combination of a gair' of spaced plates, a work. supporting p ate, means for drivin all of said plates at a uniform rate of speei a lapping plate over said work supporting plate, and adjustable means, connected to said first-mentioned pair of plates and to said lapping plate for moving said lapping plate in a strokethat ranges from a circle to a straight line, as maybe desired, as and for the purposes set forth.

8-. In a'machine of the class described,.l30

the combination of a pair of spaced plates, a work supporting plate, means for driving all of said plates at a uniform rate of speed, a lapping plate over said work supporting plate, an adjustable bar connected to one of said first-mentioned pair of plates and to said lapping plate, and an adjustable bar connected to the other first-mentioned plate and to said first-mentioned bar, as and for the purposes set forth.

9. In a machine of'the class described, the

combination of a pair of spaced plates, a

work supporting plate, means for driving all of said plates at a uniform rate of-speed, a lapping plate over said work supporting plate, a posteccentrically mounted upon one of said first-mentioned pair of plates, the remaining plate of the pair being provided with a slot extending across its top surface, a post adjustably mounted within said slot, a post mounted upon said lapping plate, an adjustable bar mountedupon said first and last mentioned posts, and an adjustable bar connected to said second-mentioned post and to said first-mentioned bar, as and for the purposes set forth.

10. Ina machine of the class described,

the combination of a pair of plates, spindles supporting said plates, bevel gears mounted upon said spindles, a shaft having bevel gears at its ends engaging said first-mentioned bevel gears, a bevel gear on said shaft intermediate its ends, a power driven means for rotating one of said first-mentioned bevel gears, whereby rotary motion is imparted to both of said plates, a work supporting plate, a pindle supporting said work supporting p ate, a bevel gear on said last mentioned spindle, a second shaft having bevel gears on its ends engaging the bevel gear on said last-mentioned spindle and the remaining bevel gear on the firstmentioned shaft, a clutch on said secondment-ioned shaft, a manually operated drive means connected to the second-mentioned shaft, a lapping plate over said work supporting plate, and means connecting said first-mentioned plates to said lapping plate, as and for the purposes set forth.

In testimony whereof I hereunto aflix my signature.

FLOYD CALVIN WEAVER. 

